I have found Tansei 探盛 in the following two books,
大日本書畫家大鑑 （傳記上編）
日本書畫鑑定大事典
with the same short one line entry:
” 探盛 外内 狩野探信守道の門人 文政頃 ”
ie. Tansei, Sotouchi, Disciple of Kanō Tanshin Moridō （Active) around Bunsei era

Sotouchi was his original family name,
Kanō Tanshin Moridō －7th gen. Kajibashi Kanō family painter 1785-1836

The reading of the seal is 藤原 Fujiwara
This seal can be seen on some works of 探雪守定
Tansetsu Morisada.